Targeted inhibition of myeloid-derived suppressor cells in the tumor microenvironment by low-dose doxorubicin to improve immune efficacy in murine neuroblastoma

Abstract

BackgroundHigh agglomeration of myeloid-derived suppressor cells (MDSCs) in neuroblastoma (NB) impeded therapeutic effects. This study aimed to investigate the role and mechanism of targeted inhibition of MDSCs by low-dose doxorubicin (DOX) to enhance immune efficacy in NB.MethodsBagg albino (BALB/c) mice were used as tumor-bearing mouse models by injecting Neuro-2a cells, and MDSCs were eliminated by DOX or dopamine (DA) administration. Tumor-bearing mice were randomly divided into 2.5 mg/kg DOX, 5.0 mg/kg DOX, 50.0 mg/kg DA, and control groups (n=20). The optimal drug and its concentration for MDSC inhibition were selected according to tumor inhibition. NB antigen-specific cytotoxic T cells (CTLs) were prepared. Tumor-bearing mice were randomly divided into DOX, CTL, anti-ganglioside (GD2), DOX+CTL, DOX+anti-GD2, and control groups. Following low-dose DOX administration, immunotherapy was applied. The levels of human leukocyte antigen (HLA)-I, CD8, interleukin (IL)-2 and interferon (IFN)-γ in peripheral blood, CTLs, T-helper 1 (Thl)/Th2 cytokines, perforin, granzyme and tumor growth were compared among the groups. The Wilcoxon two-sample test and repeated-measures analysis of variance were used to analyze results.ResultsThe slowest tumor growth (F=6.095, P=0.018) and strongest MDSC inhibition (F=14.632, P=0.001) were observed in 2.5 mg/kg DOX group. Proliferation of T cells was increased (F=448.721, P<0.001) and then decreased (F=2.047, P=0.186). After low-dose DOX administration, HLA-I (F=222.489), CD8 (F=271.686), Thl/Th2 cytokines, CD4+and CD8+lymphocytes, granzyme (F=2376.475) and perforin (F=488.531) in tumor, IL-2 (F=62.951) and IFN-γ (F=240.709) in peripheral blood of each immunotherapy group were all higher compared with the control group (all of P values < 0.05). The most significant increases in the aforementioned indexes and the most notable tumor growth inhibition were observed in DOX+anti-GD2 and DOX+CTL groups.ConclusionsLow-dose DOX can be used as a potent immunomodulatory agent that selectively impairs MDSC-induced immunosuppression, thereby fostering immune efficacy in NB.